Dynatron oscillator



March 23, 1937. p Q FARNHAM 2,074,465

DYNATRON OSCILLATOR Filed March 5, 1932 Patented Mar. 23, 1937 UNITEDSTATES DYNATRON osoILLA'ron' Paul 0. Farnham, Boonton, N.

J assignor, by

mesne assignments, to Radio Corporation of America, New York, N. Y., acorporation of Delaware Application March 5, 1932, Serial No. 597,076

2 Claims.

This invention relates to dynatron oscillators and particularly tooscillators capable of maintaining sustained oscillations at relativelyhigh frequencies.

When the energizing potentials applied to a vacuum tube are properlychosen, the tube functions as a dynatron, i. e., it has a negative plateresistance over an extended range of applied voltages and will maintainsustained oscillations so long as the parallel impedance at resonance ofthe external plate circuit load is numerically greater than the negativeplate resistance or internal plate-cathode resistance of the tube. Whileno difliculty is experienced in designing tuned plate circuit loads forthe broadcast and somewhat higher frequency ranges, it will be apparentthat the problem of designing a high resistance tuned plate load becomesincreasingly difiicult with the higher frequencies, and it has beenbelieved that the dynatron could not be operated over the highestfrequency bands.

An object of the present invention is to provide a dynatron oscillatorof the type stated that will maintain sustained oscillations atfrequencies higher than was previously possible. A further object is toprovide a dynatron oscillator including circuit elements forsupplementing the dynatron action by an external coupling between theplate and control grid. More specifically, an object is to provide anoscillator including a screen grid tube energized for operation as adynatron and in which a capacitive coupling is provided between theplate and control grid.

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanyingdrawing in which the single figure is a circuit diagram of oneembodiment of the invention.

In the drawing, the reference numeral l identifies a screen grid tubehaving a plate P connected to a source of positive potential B through atuned plate load LC and having a screen grid G2 which is subjected tohigher positive potential than that applied to the plate, for example,by

45 connection to an appropriate point on the source B. A bias resistor2, shunted by a by-pass condenser 3, is included in the cathode load andthe circuit from the cathode to the control grid G1 is completed througha leak resistance 4. Appropriate by-pass condensers 5 are provided forreturning the high frequency screen grid and plate circuits to thecathode around the direct current source B.

The circuit as so far described will be recog- 55 nized as aconventional dynatron oscillator circuit which will generateoscillations so long as the resistance of the plate load, at itsresonant frequency, is numerically greater than the internal platecathode impedance or negative resistance of the tube. In such a dynatronoscillator, an increase in control grid potential would cause anincrease in plate potential, contrary to the condition in triodeoscillators. Hence direct coupling from the plate to the control gridcircuit, i. e., without any phase reversal, may be employed to increasethe tendency toward oscillation when the plate load is tuned to highfrequencies at which oscillation does not readily occur. In accordancewith this invention, a small coupling capacity C1 is provided betweenthe plate and control grid and, preferably, the inherent capacitybetween G1 and the cathode K is supplemented by shunting an externalcapacity C2 between the control grid G1 and the grounded point of thecathode circuit.

With this arrangement, the oscillating voltage developed on the plate issplit by the voltage dividers C102, and a portion of the plate voltageis thus applied to the control grid in proper phase to maintainoscillations. This feedback between the plate and grid circuits raisesthe upper limit of the range of frequencies over which sustainedoscillations will be produced but does not sub-' stantially affect thedynatron oscillation at the lower frequencies. In fact, the introductionof the capacitive coupling affords greater latitude in the design of theoscillator circuits for use at low frequencies since it effects anactual or apparent reduction in the magnitude of the negative resistanceof the tube.

As will be apparent to those familiar with the design and constructionof oscillator circuits, other forms of coupling may be provided tosupplement the dynatron action and other types of tubes may be employed.It is to be understood that the invention is not restricted to theparticular circuit herein illustrated and described, as various changesmay be made in the several parts, their relative size, shape andrelationship, without departure from the spirit of my invention as setforth in the following claims.

I claim:

1. In an oscillator; the combination with a vacuum tube having elementsincluding a cathode cooperating with a control grid, an auxiliary coldelectrode, and a plate; means for impressing on said auxiliary electrodea higher positive potential than on the plate for producing a negativeinternal plate-cathode impedance; a tuned load in the plate circuit;means for adjusting the oscillating frequency of said tube; an externalnon-resonant capacity load between said control grid and said cathode;and an external capacity coupling between the plate and control grid ofthe tube.

2. In an oscillator, the combination with a vaccum tube having elementsincluding a cathode cooperating with a control grid, an auxiliary coldelectrode, and a plate; means for impressing on said auxiliary electrodea higher positive potential than on the plate for producing a nega- PAULO. FARNHAM.

